While searching the Web for old pictures of M27 I came across this gem; “Photographs Of Nebulae And Clusters, Made With The Crossley Reflector, Volume VIII” by James Edward Keeler, published in 1908. This may be found at…

This is a great source of pictures of deep sky objects that are over 100 years old (the pictures, not the deep sky objects). It is fascinating to copy pictures from this publication and paste them over modern pictures in Photoshop. I carefully rescale them to match the image scale and orientation of the two images and then blink them by clicking the layers on and off. You can easily spot stars with high proper motions and possible variables or asteroids. This is a great way to pass the time waiting for the weather to clear.

And yes, there are several stars near M27 that show high proper motion!

That's an excellent idea, John! (But not at all surprising about high proper motion stars.) I would be careful about jumping the gun on potential variables, though. Ye Olde Plates are more than likely to be blue-sensitive, thus making the redder stars record as rather dim.

Heh, heh, that is why I said 'potential' variables. It is really neat to blink these images. You can easily pick out stars with high proper motions, some moving in the same direction at the same rate, most not. As far as variables, I noticed one star in particular that is easy to see in the 1899 plate, but absent from my image. The star's image is nice'n round so it is not likely to be an asteroid. My first stop will be the AAVSO web site to see what variables have already been cataloged in this field.

I do this all the time with POSS I survey images and the things I shoot these days. Many stars show proper motion in the intervening 60 years. Harvard is digitizing its vast collection of glass plates to push the coverage back about 100 years.

The "I Killed Pluto" author describes writing some custom software to do initial screening for blink comparison of first plates that were made then scanned each night, then later straight digital images (they changed imagers over during the years he was doing the search). He had two people doing all the imaging, and his job was writing the filtering software and then blinking the remaining candidates on his computer screen.

I imagine there are many thousands of plates stashed around the world, some scanned, some not yet. It would be a good crowdsource / Zooniverse-type project if someone could set up a good sofware chain. Maybe the Tortilla plate solver or another automatic image alignment program first, and then automated marking of possible items of interest, then eyeballs.

Thank you for posting this link to J. E. Keeler's photographs published in 1908. I find these photos particularly valuable for my current interest in 19th century observatories. Although these photos technically belong to the 20th century, they do show something of what the 19th century observers were able to see at their scopes--keeping in mind that photographs always capture more than the human eye at the scope.